When did you do your first Gator Chomp? Can you recall seeing your first Gator Chomp? I did not realize that the gesture was created in 1981, according to Wikipedia. I do not recall seeing a Gator Chomp until the 1990s. My high school was the Gators, so I remember doing my first chomp in early 1990s high school.
How about everyone else?
Oh yes--it was at the FSU game in the then-still-named "Florida Field", day after Thanksgiving, 1980--and I was there.
I believe I have told this one before, but here is the short(ish) version:
As we arrived at the stadium that day for a mid-afternoon start (sometime between 1:30pm and 3:00pm kickoff, as I recall), members of the cheer-leading squad were waiting at key points around the place, handing out single-sheet step-by-step instructions (complete with hand-drawn pictures of each step in "The Chomp") with the repeated exhortation, "We'll do it for the first time at the start of the 2nd quarter--Let's have FUN with it!"...No one really knew what to make of it, at least us students heading in that day, but this was FSU, and we hadn't beaten them any of the years I was there, and I was a Senior. Anyway, come the 2nd quarter, the announcer directed our attention to the Gator sideline "where the Cheering Squad will lead us in our inaugural Gator Chomp!", and further instructed the crowd in what they and the band would be doing to "support" us. I believe the score at the time was Gators 7, 'Noles 3.
Anyway, the cheerleaders demonstrated/led us from the "opening position", and the Band commenced that "Jaws"-like theme for the very first time. The crowd, the whole stadium, had stood for this, and quite solemly and with focused determination to get-it-right, began shooting up its right arms high and left arms low and CLAPPING once on the beat, slow at first, then faster and faster in perfect unison...I swear it looked like the Nuremburg Rallies, for goodness sakes--The Seminole players both on the field and sidelines were looking around in complete and baffled bewilderment; you could tell it rattled them, they just didn't know what to make of it.
It did more than that, as it turned out. They came completely unglued...From that point on the game became a blow-out. Having come in thoroughly confident they had our number, they never even threatened to score again--while we just had a field day. We did "the Chomp" one more time early in the 4th, but by then it was more celebration: we HAD them, it was long over, and a Gator tradition was born. Oh yeah...Final Score, Gators 35, Semi-holes 3.
I am saving my first for my FIRST real gator football games I go to! 
(laughing) Hey, ANYONE of us who says they haven't done it alone to the TV-set in the heat of a game, especially in the Tebow days, or late-game back-at-a-player after a score, etc. is LYING!